The term "sweater" is a catch-all for various types of garments.
A fundamental division is between a cardigan and a pullover . If the sweater has no sleeves, it is generally called a sweater vest or tank top, or, in the UK, very commonly a "sleeveless pullover" which will very usually have a V neck and can be worn semi-formally; in UK parlance such a sleeveless garment would only be called a "tank top" if it had a square or scooped neck and a generally juvenile appearance.; a "vest" in British English refers to the same item as "undershirt" in American English.
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